The disclosed invention relates to manufacturing of steel in electric arc furnaces in ferrous metallurgy.
During the work of the electric arc furnace the energy necessary for metal melting is supplied by the electrode column formed as a set of electrodes joined by threaded nipples. With wear of the electrode, the electrode column is elongated periodically by means of screwing together a new electrode and a nipple, prepared in advance, with the active electrode of the said column.
Being dependent on the method of periodic elongation of the electrode of the electrode column and on the applied nipple and electrode, the specific character of the current flow through the electrode joint (connection) determines, in its turn, the heat released in this part of the electrode column and, consequently, the heating-up of the electrode in the process of its operation. High heating-up temperatures of the electrode in the electric arc furnace considerably enhance its wear and increase the use of costly electrodes per ton of steel made. The method of preliminary preparation of the electrode plays a significant role for the practical realization of the method of periodic elongation of the electric arc furnace electrode.
There is known a method for periodic elongation of the electrode for the electric arc furnace, that includes screwing an earlier prepared biconic threaded nipple onto the active electrode of the electrode column (for example, see “The CESO processing chain for the optimization of the graphite electrode columns”. News and Recommendations for AC and DC Arc Furnace Applications by firm SGL CARBON GROUP, January, 1999, p. 3-6).
By means of controlling the process of screwing together the electrodes that are being connected, the known method proposes to solve the problem of reducing the prestressing force of the electrode connection that decreases the working capacity of the electrodes.
The main drawback of the known method consists in leaving the traditional way the current flows through the joint “electrodes-nipple” unchanged. Thus, the known method does not solve the problem of easing the current flow at the joint “electrodes-nipple”, which leads to increased heat release in this part of the electrode arc due to additional resistance in the contacts “electrode-nipple-electrode”. High heating-up temperatures of electrodes enhance their wear.
There is known a method for periodic elongation of the electric arc furnace electrode, that includes screwing onto the active electrode of the electrode column an earlier prepared new electrode and a threaded nipple, having a longitudinal through hole in which the material with lower melting temperature than the working temperature of the electrode in the furnace is placed (see, for example, patent of the FRG No 2203226, H05 B7/14 dated Jan. 24, 1972). The material being placed into the through hole of the nipple is resin which during the work of the electric arc furnace cokes and joints the electrodes and the nipple in a single unit.
Considering its main characteristics, the known method for periodic elongation of the electrode is the closest to the one disclosed, due to which the said known method was adopted as a prototype.
The substantial drawback of the known method consists in its low effectiveness in terms of reducing electric resistance in the joint “acting electrode-nipple-new electrode”. The mentioned drawback is determined by the fact that the coking material, formed from the resin, and the materials of the electrode and the nipple are, in the end, of the same nature, which means practically the same electric resistance characteristics. Consequently, the realization of the said known method leads to a slight decrease in the energy released in the joint under consideration—“electrodes-nipple”—and thus the electrode warms up considerably in the working area of the electric arc furnace.
The disclosed method for periodic elongation of the electric arc furnace electrode is free of the mentioned drawbacks. It provides for an essential reduction in resistance to the electric current flow in the junction “joined electrodes-nipple”. Thus the energy, released in the junction because of the electric current flow, is reduced, due to which the decrease in the heating-up temperature of the elements being joined in the electric arc furnace is attained. Thereby three reasons of the electrode wear are reduced: side surface oxidation, mechanical failures, stub-end losses.
The named technical results are obtained because in the method for periodic elongation of the electric arc furnace electrode, that includes screwing onto the active electrode of the electrode column an earlier prepared new electrode and a threaded nipple having a longitudinal through hole in which the material with lower melting temperature than the working temperature of the electrode in the furnace is placed, according to the invention a metal rod having specific electric resistance a few orders of magnitude lower than the one of the electrode and the nipple materials is inserted into the nipple cavity, while the volume of the said metal rod is chosen so as to provide, after its melting, complete filling up with liquid metal of cavities formed between the nipple and the acting electrode after they have been screwed together, the cavity of the longitudinal through hole in the nipple and the cavity between the nipple and the threaded socket bottom of the new electrode, as well as partial filling of the additional cavity provided for in the threaded bottom of the new electrode, the gas mixture formed in the space of the additional cavity of the new electrode which is free of liquid metal being drawn into the working area of the furnace through special holes in the body of the electrode.
There is known an electric arc furnace electrode, having a threaded socket on both its sides and a specifically shaped cavity in the bottom part of the socket (see, for example, U.S. Pat. No. 4,161,169 dated Nov. 11, 1977 r., H05 B7/14).
The disadvantage of the known electrode is the lack of the technical solution for easing the electric current flow through the joints “electrodes-nipple” after its joining with the active electrode of the electric arc furnace.
There is known an electric arc furnace electrode having threaded sockets on both sides of the electrode that end up with a threadless section (see, for example, the Russian Federation patent No 2037984, H05 B7/14 dated Jul. 14, 1992 r., published Jun. 19, 1995. Bull. No 17).
Considering its main characteristics, the said known electrode is the closest to the disclosed electrode due to which it was adopted as a prototype.
The disadvantage of the known electrode is the lack of the technical solution in its design for easing the electric current flow through the joints “electrodes-nipple” after its joining with the active electrode of the electric arc furnace. As a result, functioning of the electrode in the electric arc furnace results in higher resistance to the electric current flow in the joint and release of additional energy that leads to greater heating-up of the junction and the nipple. The latter makes the working conditions of the electrode worse and decreases its performance.
The disclosed electrode is free of the mentioned drawbacks. Its design provides for a technical solution that allows the resistance to the electric current flow in the junction “electrodes-nipple” to be decreased significantly after joining the electrode to the electric arc column. This allows decreasing the general heating-up temperature level of the electrodes and the nipple in their junction and, based on this, reducing the factors of increased electrode wear.
The enumerated technical results are obtained because of the fact that for the realization of the method for periodic elongation of the electric arc furnace electrode, the electrode, having on both its sides threaded sockets ending up with additional threadless sections, according to the invention is equipped with additional threadless cavities—at the bottom of the threaded socket, in the middle, at least on one side of the electrode and at most on its both sides, the depth and the diameter of the said cavity on one of the sides of the electrode having larger values and the cavity being connected to the external surface of the electrode by means of holes. Meanwhile the holes connecting the additional cavity with the external surface of the electrode are inclined, performed at an angle to the other side of the electrode.
There is known a method for preliminary preparation of the electrode for the accomplishment of periodic elongation of the electric arc furnace electrode, including screwing together the electrode and the nipple having a longitudinal through hole into which a substance with the melting temperature lower than the working temperature of the electrode in the furnace is placed (see, for example, the already mentioned patent of the FRG No 2203226).
Considering its main characteristics, the said known method is the closest to the one disclosed due to which it was adopted as a prototype.
The advantages of the known method include a noticeable simplification of the procedure for periodic elongation of the electrode under the industrial conditions of the electric arc furnace operation. However, the known method has a significant drawback consisting in the fact that the process of preliminary preparation of the electrode in this method includes no methods for considerably decreasing the resistance to the electric current flow in the junction “electrodes-nipple” during the work of the electrode in the electric arc furnace. The said drawback prevents reducing the temperatures up to which the electrode is heating up in this junction, which, in its case, diminishes its performance.
The disclosed method for preliminary preparation of the electrode uses the mentioned advantages of the known method, but is free of its drawbacks. It provides for realizing the techniques that allow, while operating the electrode in the electric arc furnace, an essential decrease in the electrode heating-up temperatures at the junction “electrodes-nipple” and an increase in the performance of the electrode on this base.
The enumerated technical results are attained due to the fact that in the method for preliminary preparation that includes screwing together the electrode and the nipple with a longitudinal through hole into which a substance with the melting temperature lower than the working temperature of the electrode in the furnace is placed, according to the invention into the additional electrode cavity connected by means of holes to the external surface of the electrode, and into the longitudinal through hole of the nipple a two-stage metal rod is installed, the rod stage with greater diameter being placed in the said cavity and compressed to the nipple, while the smaller diameter rod stage being placed in the nipple hole. In addition, the said metal rod is compressed to the nipple by means of a spring made of the same material as the rod. Moreover, the said metal rod is compressed to the nipple by means of metal swarf and (or) granules made of the same material as the rod. Also the said metal rod is compressed to the nipple by means of packing substance that burns out under the working temperature of the electrode in the electric arc furnace.